The term "polyphenylene ether resin" includes a family of polymers that are well known to those skilled in the art. These polymers are made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derivatives thereof. By way of illustration, certain of the polyphenylene ethers are disclosed in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, and in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358. In the Hay patents, the polyphenylene ethers are prepared by an oxidative coupling reaction comprising passing an oxygen-containing gas through a reaction solution of a phenol and a metal-amine complex catalyst.
Other disclosures relating to processes for preparing polyphenylene ether resins, including graft copolymers of polyphenylene ethers with styrene type compounds, are found in Fox, U.S. Pat. No. 3,356,761; Sumitomo, U.K. Pat. No. 1,291,609; Bussink et al, U.S. Pat. Nos. 3,337,499; Blanchard et al, 3,219,626; Laakso et al, 3,342,892; Borman, 3,344,166; Hori et al, 3,384,619; Faurote et al, 3,440,217; and disclosures relating to metal based catalysts which do not include amines, are known from U.S. Pat. Nos. such as Weiden et al, 3,442,885 (copperamidines); Nakashio et al, 3,573,257 (metal-alcoholate or -phenolate); Kobayashi et al, 3,455,880 (cobalt chelates); and the like. In the Stamatoff patents, the polyphenylene ethers are produced by reacting the corresponding phenolate ion with an initiator, such as peroxy acid salt, an acid peroxide, a hypohalite, and the like, in the presence of a complexing agent. Disclosures relating to non-catalytic processes, such as oxidation with lead dioxide, silver oxide, etc., are described in Price et al, U.S. Pat. No. 3,382,212. Cizek, U.S. Pat. No. 3,383,435 discloses polyphenylene ether styrene resin compositions. Katchman, U.S. Pat. No. 3,663,661 also discloses polyphenylene ether resin compositions. All of the above-mentioned disclosures are incorporated herein by reference.
Compositions of polyphenylene ethers are known to exhibit inferior thermal properties after exposure to thermal stress for prolonged periods. This form of degradation causes molded articles to become brittle and fail when they are subjected to stress. This has resulted in a need for stabilizers that prevent embrittlement of polyphenylene ether resin compositions when said composition are used in high temperature applications. Applicant has now discovered that diphenylamines may be employed to provide stabilized compositions of polyphenylene ether resins without any evidence of incompatibility. This stabilization is accomplished without discoloration of the polyphenylene ether resin which is an important consideration for white or pastel colored articles. The diphenylamines have been employed in the stabilization of rubber, polyamides, polyacetals, polyethylene, polypropylene, ethylene-propylene copolymers and terpolymers, ABS and synthetic lubricants. These materials are processed at much lower temperatures than the polyphenylene ether resins and it is surprising that the diphenylamines, at low concentrations, are effective to stabilize polyphenylene ether resin compositions which are processed at relatively high temperatures, i.e., 580.degree. F.
Accordingly, it is a primary object of this invention to provide polyphenylene ether resin compositions that have improved resistance to thermal aging.
It is also an object of this invention to provide a new method for imparting thermal stability to a polyphenylene ether resin composition.